Conventionally, transmissive liquid crystal display devices are known as image display means. The transmissive liquid crystal display device is provided with a non-self-luminous liquid crystal panel and thus requires a backlight device. In such a backlight device, a cold cathode fluorescent lamp (CCFL) has been used as a light source. Recently, however, a backlight device including a LED as a light source is widely used, which is free from disadvantages of a cold cathode fluorescent lamp, such as environmental pollution caused by mercury, or slower response speed. In addition to solving the disadvantages of a cold cathode fluorescent lamp, the backlight device including a LED as a light source can also achieve a partial drive such as local dimming to improve a contrast ratio of an image. The local dimming will be described below.
The “local dimming” is a process in which (i) a backlight device is divided into segments (blocks) each having its light source and (ii) a light intensity of each of the segments is adjusted based on a luminance component of an image to be displayed in a corresponding area of a liquid crystal panel, which corresponding area is irradiated with light emitted from the segment. That is, in the liquid crystal display device which employs local dimming, a light intensity of a segment corresponding to an area displaying a bright image can be increased, whereas a light intensity of a segment corresponding to an area displaying a dark image can be decreased. The liquid crystal display device which employs local dimming can thus display an image of a higher contrast ratio in which a bright image displaying area is displayed brighter and a dark image displaying area is displayed darker.
However, the liquid crystal display device which employs local dimming has a disadvantage described below, in a case where, for example, one area displaying white and black images and another area displaying only a black image are adjacent to each other. That is, a light intensity of a segment corresponding to the area displaying white and black images is adjusted to a value in accordance with the white image (with high luminance), whereas a light intensity of a segment corresponding to the area displaying only a black image is adjusted to a value in accordance with the black image (with low luminance). This leads to a difference in brightness of displayed black between one area and another area, resulting in an unnaturally-appearing image being displayed in which a boundary between the areas is conspicuous.
In order to avoid such a disadvantage, a liquid crystal display device has been proposed, in which light intensities of respective segments are determined by (i) calculating light intensities of the respective segments on the basis of a local dimming technique and then (ii) correcting the light intensities of the respective segments so that no segment has a light intensity differing greatly from those of adjacent segments. As an example, Patent Literature 1 discloses a technique in which a luminance is gradually changed for each of adjacent areas.
Meanwhile, multi-display devices, each of which includes a plurality of image displaying means set in array, have been widely used. Such multi-display devices encompass a multi-display device of screen projection type as follows: Patent Literature 2 discloses a technique to prevent light emitted by one of adjacent projectors from being displayed on a screen corresponding to the other of the adjacent projectors, so that adjustment between screens can be easily carried out. Patent Literature 3 discloses a technique in which (i) enlarged images for respective of a plurality of displays are projected such that the enlarged images partially overlap each other, and (ii) a luminance of an overlap image area and a luminance of a non-overlap image area are controlled to be equal to each other so as to eliminate a difference in luminance in the overlap part. Patent Literature 4 discloses a technique in which (i) an original image is divided into a plurality of areas and (ii) a projection image corresponding to the original image is obtained on a single screen by combining images of the respective plurality of areas while partially overlapping adjacent images.